Piezo ultrasound devises provide ultrasonic emissions to measure the thickness of materials, particularly metal. High temperature causes these electronic devises to become erratic and unreliable.
At present it is generally necessary to protect the piezo probe by using delay lines or delay blocks, which are devices that allow the ultrasonic probe to be in contact with the elevated temperature surface material for a longer period of time.
In practice, the probes are not held on the elevated temperature surface for more than a few seconds before they heat up and become erratic or are damaged. Since these are hand held devices, the operator cannot hold his hand steady and in place long enough for an accurate reading to be made.
On repeated contacts on the elevated temperature surface, the piezo probe becomes so over heated that its readings are not correct. Therefore, this method of measuring on a elevated temperature surface is not reliable or safe.